Estimation device, system, estimation method, and program

Abstract

A technology is provided that can accurately estimate the instantaneous internal resistance of a storage element. [Solution] The estimation device is an estimation device that estimates the internal resistance of a storage element in a storage system, wherein the storage system is configured by connecting multiple storage element groups in parallel, each group including multiple storage elements and a circuit breaker that interrupts the current flowing through the storage elements, and the estimation device is equipped with a processing unit that acquires the voltage behavior of the storage elements when the circuit breaker is opened or closed while the storage system is being charged or discharged, and executes a process to estimate instantaneous resistance that indicates the instantaneous internal resistance of the storage elements based on the acquired voltage behavior of the storage elements.

Description

[Technical Field]

[0001] The present invention relates to an estimation device, a system, an estimation method, and a program. [Background technology]

[0002] The use of energy storage systems equipped with multiple energy storage elements is expanding to stabilize and effectively utilize the electricity generated by power generation systems such as solar power generation systems and wind power generation systems. Repeated charging and discharging of energy storage elements increases their internal resistance and reduces their capacity, resulting in degradation. When operating an energy storage system, it is important to understand the internal resistance and degradation state of the energy storage elements.

[0003] The battery evaluation device disclosed in Patent Document 1 measures the response characteristics of the voltage of the storage device when the storage device is in a charging / discharging state, but the charging / discharging command value enters a dead zone where no charging or discharging occurs, and charging / discharging is stopped, and evaluates the deterioration state of the storage device based on the response characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6431644 Summary of the Invention [Problem to be solved by the invention]

[0005] As the use of energy storage systems expands, more precise control is expected, and control using internal resistance and energy storage element models is becoming more common. In the case of energy storage systems that are used over long periods, such as 10 to 20 years, the internal resistance of the energy storage elements changes significantly over time. To improve control accuracy, it is necessary to accurately estimate the internal resistance.

[0006] An object of the present disclosure is to provide a technique that can accurately estimate the instantaneous internal resistance of an energy storage element. [Means for solving the problem]

[0007] An estimation device according to one aspect of the present disclosure is an estimation device that estimates the internal resistance of a storage element in a storage system, wherein the storage system is configured by connecting multiple storage element groups in parallel, each group including multiple storage elements and a circuit breaker that interrupts current flowing through the storage elements, and the estimation device includes a processing unit that acquires the voltage behavior of the storage elements when the circuit breaker is opened or closed while the storage system is being charged or discharged, and performs a process to estimate instantaneous resistance that indicates the instantaneous internal resistance of the storage elements based on the acquired voltage behavior of the storage elements. [Effects of the Invention]

[0008] According to the present disclosure, the instantaneous internal resistance of an energy storage element can be estimated with high accuracy. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an estimation system. [Figure 2] 1 shows an example of the configuration of a container of a power storage system. [Figure 3] 2 shows an example of an electrical connection configuration of a power storage system. [Figure 4] FIG. 2 is a block diagram showing an example of the configuration of a bank BMU. [Figure 5] 4 shows the voltage-time profile of the storage element. [Figure 6] 1 shows an example of the time variations in SOC, voltage, and current of a storage element during operation. [Figure 7] 10A and 10B are diagrams illustrating a method for estimating instantaneous resistance according to the present embodiment. [Figure 8] 10 is a flowchart showing an example of a processing procedure executed by a bank BMU. [Figure 9] 10 is a flowchart showing an example of a processing procedure executed by a bank BMU. [Figure 10] 10 shows an example of an electrical connection configuration of a power storage system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (1) An estimation device according to one aspect of the present disclosure is an estimation device that estimates the internal resistance of a storage element in a storage system, the storage system being configured by connecting multiple storage element groups in parallel, each group including multiple storage elements and a circuit breaker that interrupts current flowing through the storage elements, and including a processing unit that acquires the behavior of the voltage of the storage elements when the circuit breaker is opened or closed during charging or discharging of the storage system, and executes a process to estimate an instantaneous resistance that indicates the instantaneous internal resistance of the storage element based on the acquired behavior of the voltage of the storage element.

[0011] The estimation device described in (1) above can accurately estimate the instantaneous resistance of a storage element based on voltage data of the storage element in which current fluctuations occur due to the opening and closing of a circuit breaker during charging or discharging of the storage system. In this specification, "instantaneous resistance" refers to a resistance component that causes an instantaneous voltage fluctuation that appears immediately after a current fluctuation. The instantaneous resistance may include ohmic resistance or charge transfer resistance. Even in a storage system that does not exhibit abrupt voltage changes suitable for calculating instantaneous resistance during normal operation, abrupt current fluctuations can be generated by intentionally opening or closing a circuit breaker during charging or discharging. In this way, voltage behavior suitable for calculating instantaneous resistance can be obtained. Since it is known that the current value is approximately zero when the circuit breaker is opened, current measurement is not required to calculate the instantaneous resistance, and simultaneous voltage and current measurements are also unnecessary, making the estimation process easier.

[0012] (2) The estimation device of (1) above may acquire the behavior of the voltage of the storage element when the circuit breaker is opened for a predetermined period of time and then closed while the storage system is being charged or discharged.

[0013] According to the estimation device of (2) above, the recovery characteristics (relaxation characteristics or return characteristics) of the instantaneous resistance can be estimated based on the voltage behavior associated with opening the circuit breaker, and the polarization characteristics (going characteristics) of the instantaneous resistance can be estimated based on the voltage behavior associated with closing the circuit breaker, thereby enabling a more detailed estimation of the internal state of the storage element.

[0014] (3) The estimation device of (1) or (2) above may output an instruction to open or close the circuit breaker, and acquire the behavior of the voltage of the storage element when the instruction is output.

[0015] The estimation device described in (3) above can control the operation of the circuit breaker by outputting an open or close command (electrical signal), so it can accurately obtain voltage behavior corresponding to the control timing, further improving the estimation accuracy of instantaneous resistance. Since the circuit breaker can be easily opened and closed without relying on human labor, the frequency of estimation can be increased.

[0016] (4) In the estimation device according to any one of (1) to (3) above, the instantaneous resistance may include an ohmic resistance and a charge transfer resistance.

[0017] According to the estimation device of (4) above, the ohmic resistance and the charge transfer resistance of the storage element can be distinguished and estimated from the instantaneous voltage fluctuation, and therefore the internal state of the storage element can be accurately grasped.

[0018] (5) Any one of the estimation devices (1) to (4) above may acquire the behavior of the voltage of the storage element when the circuit breaker of one of the storage element groups in the storage system is opened or closed.

[0019] According to the estimation device of (5) above, the power supply to only one of the plurality of storage element groups is cut off, so that the instantaneous resistance of the desired storage element can be appropriately estimated while ensuring the charging and discharging capacity of the entire storage system.

[0020] (6) Any one of the estimation devices described in (1) to (5) above may estimate the instantaneous resistance of each of the storage elements at different SOCs.

[0021] The estimation device of (6) above can estimate instantaneous resistances corresponding to different SOCs (States of Charge), so that instantaneous resistances that depend on the SOC can be calculated more accurately. By calculating instantaneous resistances corresponding to various SOCs, the accuracy of various processes using the obtained instantaneous resistances can be improved.

[0022] (7) The estimation device according to any one of (1) to (6) above may determine whether or not the circuit breaker has a fault based on a behavior of the voltage of the storage element.

[0023] According to the estimation device of (7) above, the acquired voltage behavior can be used to estimate the instantaneous resistance and determine whether or not there is a fault in the circuit breaker, i.e., self-diagnosis of the circuit breaker can be performed, thereby improving the maintainability of the energy storage system.

[0024] (8) In the estimation device according to any one of (1) to (7) above, the circuit breaker may be a DC / DC converter. In this specification, the term "circuit breaker" includes a DC / DC converter.

[0025] According to the estimation device of (8) above, it is possible to control the voltage using a circuit breaker. Since the voltage of the multiple storage elements in the storage element group can be appropriately controlled using a DC / DC converter, it is possible to make the current flowing through the multiple storage elements connected in series the same. For example, even if the storage elements are prone to SOC imbalances, such as iron phosphate lithium-ion batteries, by passing the same current through each storage element, it is possible to suppress the occurrence of imbalances between the storage elements.

[0026] (9) A system according to one aspect of the present disclosure includes a group of multiple energy storage elements connected in parallel, and an estimation device, wherein the group of energy storage elements includes multiple energy storage elements and a circuit breaker that interrupts current flowing through the energy storage elements. The estimation device includes a processing unit that acquires voltage behavior of the energy storage elements when the circuit breaker is opened or closed while the group of energy storage elements is being charged or discharged, and that executes processing to estimate instantaneous resistance indicating instantaneous internal resistance of the energy storage elements based on the acquired voltage behavior of the energy storage elements.

[0027] (10) An estimation method according to one aspect of the present disclosure is a method for estimating the internal resistance of a storage element in a storage system, the storage system being configured by connecting multiple storage element groups in parallel, each group including multiple storage elements and a circuit breaker that interrupts current flowing through the storage elements, and while the storage system is charging or discharging, the method acquires the behavior of the voltage of the storage elements as the circuit breaker is opened or closed, and estimates an instantaneous resistance indicating the instantaneous internal resistance of the storage elements based on the acquired behavior of the voltage of the storage elements.

[0028] (10) A program according to one aspect of the present disclosure is a program for estimating the internal resistance of a storage element in a power storage system, the power storage system being configured by connecting multiple groups of storage elements in parallel, each group including multiple storage elements and a circuit breaker that interrupts current flowing through the storage elements, and causing a computer to acquire the voltage behavior of the storage elements when the circuit breaker is opened or closed while the power storage system is being charged or discharged, and to execute a process of estimating instantaneous resistance indicating the instantaneous internal resistance of the storage elements based on the acquired voltage behavior of the storage elements.

[0029] The present disclosure will be specifically described with reference to the drawings showing embodiments thereof.

[0030] (First embodiment) 1 is a schematic diagram of an estimation system 100. The estimation system 100 includes a power storage system 1. The power storage system 1 is configured by a container 11 that houses a plurality of power storage elements. The number of containers 11 may be plural.

[0031] The power storage system 1 is, for example, an ESS (Energy Storage System) and is used in a power generation system PG such as a solar power generation system, a wind power generation system, a hydroelectric power generation system, a biomass power generation system, a geothermal power generation system, or a thermal power generation system. The power storage system 1 stores power supplied from the power generation system PG and supplies the stored power to a load PC. The load PC includes power consumption facilities such as factories, office buildings, schools, hospitals, restaurants, and airports.

[0032] The power storage system 1 may be connected (grid-interconnected) to a power grid PS and used to suppress voltage fluctuations and frequency fluctuations in the power grid PS. The power storage system 1 may be installed on the premises of a power consumer, such as a factory, and used for energy management such as BCP (Business Continuity Plan) measures and peak shifting, or for power trading in the power market. The power storage system 1 may be used as a backup power system (emergency power system). The power storage system 1 is not limited to industrial use, and may also be for home use.

[0033] A power converter 2 is installed between the power storage system 1 and the power generation system PG and load PC. The power converter 2 is also called a PCS (Power Conditioning System). The power converter 2 converts the power (AC power or DC power) supplied from the power generation system PG into DC power of a predetermined magnitude and supplies the converted DC power to the power storage system 1. The power storage system 1 stores the power supplied from the power generation system PG via the power converter 2. The power storage system 1 supplies the stored power to the load PC in response to an external request. The power supplied from the power storage system 1 to the load PC is converted from DC power to AC power by the power converter 2.

[0034] 1, the power converter 2 is installed outside the power storage system 1. Alternatively, the power converter 2 may be installed inside the power storage system 1.

[0035] The power storage system 1 may be connected to a monitoring server 3 via a communication network NW such as the Internet. The monitoring server 3 is an information processing device capable of various information processing and sending and receiving information, such as a server computer, a personal computer, or a quantum computer. The monitoring server 3 collects various data related to the power storage system 1 through communication and remotely monitors the power storage system 1. The communication network NW may be a local network for the manufacturer or maintenance company of the power storage system 1. The monitoring server 3 may be a local computer provided near the power storage system 1.

[0036] 2 shows an example of the configuration of a container 11 of the power storage system 1. The container 11 houses a plurality of power storage panels 12. Although not shown, the power storage system 1 may be configured by omitting the container 11 and installing a plurality of power storage panels 12 outdoors. The container 11 may also house auxiliary equipment such as an air conditioner and lighting equipment.

[0037] Each of the power storage panels 12 includes a plurality of banks 14. Each bank 14 is configured by electrically connecting a plurality of power storage modules 15 in series. The banks 14 are connected in parallel with one another. A configuration in which a plurality of banks 14 are connected in parallel is also called a domain. The number of banks 14 included in the power storage panel 12 and the number of power storage modules 15 that make up each bank 14 are selected arbitrarily. Although the power storage panel 12 in FIG. 2 includes one domain, it may include a plurality of domains.

[0038] The power storage module 15 is configured by connecting a plurality of power storage cells in series. In one example, the power storage cells are battery cells based on lithium-ion secondary batteries. Alternatively, the power storage cells may be battery cells based on all-solid-state batteries, lead batteries, redox flow batteries, zinc-air batteries, alkaline manganese batteries, lithium-sulfur batteries, sodium-sulfur batteries, silver-zinc oxide batteries, nickel-metal hydride batteries, molten salt thermal batteries, or the like, or may be capacitors. The number of power storage cells constituting the power storage module 15 can be selected arbitrarily. The power storage cells or the power storage module 15 are an example of a power storage element, and the bank 14 is an example of a group of power storage elements.

[0039] Fig. 3 shows an example of an electrical connection configuration of the power storage system 1. Fig. 3 shows the electrical connection configuration of one power storage board 12 included in the power storage system 1. The power storage system 1 includes a plurality of banks 14, a plurality of bank BMUs (Battery Management Units) 17 provided corresponding to each bank 14, a domain BMU 18, and a communication device 19. The domain BMU 18 and the communication device 19 are separate from the power storage board 12 and may be housed in a control board built into the container 11. For ease of explanation, three banks 14 are shown in Fig. 3, but a large number of banks 14, for example, 20, may be built into the power storage board 12. One bank 14 includes, for example, 250 series-connected power storage cells.

[0040] The banks 14 are connected to the outside (such as the power converter 2, a power supply source, and a power supply destination) via power lines 41. The power lines 41 have a main path connected to the outside and branch paths that branch off from the main path at branch points and are connected to each bank 14. The banks 14 store (charge) power supplied via the power converter 2 and the power lines 41, and supply (discharge) the stored power to the external power supply destinations via the power lines 41 and the power converter 2.

[0041] In addition to the bank BMU 17, each bank 14 includes a circuit breaker 42 for interrupting the flow of current to the bank 14, a voltage sensor 43 for measuring the voltage of the storage cell, and a current sensor 44 for measuring the current flowing through the storage cell.

[0042] The voltage sensor 43 measures the voltage of each energy storage cell over time. The current sensor 44 is, for example, a Hall sensor, and measures the current flowing through each bank 14 over time. A plurality of voltage sensors 43 and current sensors 44 may be provided. For example, a voltage sensor 43 may be provided for each energy storage module 15. Although not shown, the bank 14 may also be provided with other sensors, such as a temperature sensor that measures the temperature of the energy storage cell. Each sensor can repeatedly acquire measurement values ​​at an appropriate period. Measurement data such as the voltage, current, and temperature of the energy storage cell measured by the voltage sensor 43, current sensor 44, and temperature sensor is output to the bank BMU 17. The measurement data may be transmitted to the bank BMU 17 via a control board that is provided for each energy storage module 15 and has a communication function that complies with a predetermined communication protocol.

[0043] The circuit breaker 42 is provided in the branch path and connects or disconnects the charge / discharge path (current path) between the bank 14 and the outside. The circuit breaker 42 is configured by, for example, an electromagnetic contactor suitable for interrupting large currents, a semiconductor switch such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), or a switch such as a relay. By closing the circuit breaker 42, the energy storage element connected in series to the circuit breaker 42 is charged or discharged, i.e., current is passed through. By opening the circuit breaker 42, it is possible to block current from flowing out from the energy storage element connected in series to the circuit breaker 42 to the outside and current from flowing in from the outside to the energy storage element.

[0044] The bank BMU 17 is a device for monitoring the state of the bank 14. The bank BMU 17 acquires measurement data such as the voltage, current, and temperature of the storage cells, and performs processing to calculate the internal resistance, SOC, and other data of the storage cells in the bank 14 based on the acquired measurement data, thereby monitoring the state of the bank 14 at each time. The bank BMU 17 in this embodiment corresponds to an estimation device that executes processing related to estimating instantaneous resistance.

[0045] The domain BMU 18 is a device for monitoring the overall status of the domain and the bank 14. The domain BMU 18 is communicatively connected to the bank BMU 17 of each bank 14. The domain BMU 18 aggregates measurement data from the bank BMU 17 of each bank 14 belonging to the domain. An existing communication standard such as CAN (Controller Area Network) is used for communication between the domain BMU 18 and each bank BMU 17. Alternatively, communication standards such as LIN (Local Interconnect Network), ECHONET (registered trademark), and ECHONET Light (registered trademark) may be used.

[0046] The communication device 19 has an interface for connecting to the communication network NW and securely transmits data to the monitoring server 3 wirelessly or via a wired connection. The communication device 19 may be, for example, a network interface card. The domain BMU 18 transmits measurement data of the energy storage elements acquired from each bank BMU 17 to the monitoring server 3 via the communication device 19. The domain BMU 18 or the communication device 19 may hold measurement data for a predetermined period of time and transmit the measurement data to the monitoring server 3 at predetermined time intervals.

[0047] 4 is a block diagram showing an example of the configuration of the bank BMU 17. The bank BMU 17 is a computer, and includes a processing unit 171, a storage unit 172, a communication unit 173, and an input / output unit 174.

[0048] The processing unit 171 includes one or more processors, such as a central processing unit (CPU) or a microprocessing unit (MPU). The processing unit 171 includes a memory, such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), which is a temporary storage medium. The processing unit 171 may include functions such as a timer that measures the elapsed time from when a measurement start instruction is given until when a measurement end instruction is given, a counter that counts numbers, and a clock that outputs date and time information. The CPU or the like included in the processing unit 171 reads and executes various computer programs stored in the storage unit 172 to control each hardware unit and cause the entire device to function as the estimation device of the present disclosure. The processing unit 171 may be realized by software, or part or all of it may be realized by hardware, such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

[0049] The storage unit 172 includes a nonvolatile storage device such as a hard disk or a flash memory. The storage unit 172 may be separate from the bank BMU 17 and may be one or more external storage devices connected externally. The storage unit 172 stores various computer programs and data referenced by the processing unit 171. The storage unit 172 of this embodiment stores a program 1P for causing a computer to execute processing related to estimation of the internal resistance of the energy storage element.

[0050] The storage unit 172 may store measurement data including the voltage, current, and temperature of the energy storage element, model information related to the energy storage element model used to control the energy storage element, etc. The model information includes, for example, configuration information indicating the circuit configuration of the energy storage element model, values ​​of the resistance elements and capacitance elements that configure the energy storage element model, etc.

[0051] A computer program (program product) including program 1P may be provided by a non-transitory recording medium 1A on which the computer program is readably recorded. Recording medium 1A is a portable memory such as a CD-ROM, a USB memory, or an SD (Secure Digital) card. Processing unit 171 reads a desired computer program from recording medium 1A using a reading device (not shown) and stores the read computer program in memory unit 172. Alternatively, the computer program may be provided via communication. Program 1P may be a single computer program or may be composed of multiple computer programs. Program 1P may also be executed on a single computer or may be executed cooperatively by multiple computers.

[0052] The communication unit 173 includes a communication device that realizes communication according to a predetermined communication standard. The processing unit 171 transmits and receives data to and from the domain BMU 18 via the communication unit 173.

[0053] The input / output unit 174 includes an input / output interface for connecting an external device, and is connected to the input / output unit 174 with a circuit breaker 42, a voltage sensor 43, a current sensor 44, and the like.

[0054] In this embodiment, the bank BMU 17 is the estimation device. Alternatively, the domain BMU 18 may function as the estimation device, or the monitoring server 3 may function as the estimation device. When the estimation device is provided at a location remote from the power storage system 1, the estimation device may receive measurement data from the power storage system 1 via communication and transmit information corresponding to the received measurement data to the power storage system 1.

[0055] The estimation device may be a single computer, or may be a computer system configured with multiple computers and peripheral devices, etc. The estimation device may be a virtual machine whose entity is virtualized, or may be a cloud.

[0056] A method for estimating instantaneous resistance according to this embodiment will now be described. The energy storage system 1 cuts off the power supply to a specific bank 14 for a predetermined period of time by opening and closing the circuit breaker 42 in that specific bank 14 among the multiple banks 14 connected in parallel while the energy storage system 1 is charging or discharging. The bank BMU 17 estimates the instantaneous resistance, which indicates the instantaneous internal resistance of the energy storage element, based on the behavior of the voltage of the energy storage element when the power supply is cut off.

[0057] In estimating the instantaneous resistance, it is preferable that the circuit breaker 42 to be controlled to open or close is the circuit breaker 42 of any one of the multiple banks 14. The selection of the target bank 14 and the timing of the estimation process may be adjusted by the domain BMU 18, the monitoring server 3, or the like.

[0058] Figure 5 shows the voltage-time profile of an energy storage element. In Figure 5, the horizontal axis represents time (sec) and the vertical axis represents voltage (V). The internal resistance of an energy storage element is expressed as the sum of the OCP (Open Circuit Potential) parameter, ohmic resistance R0, charge transfer resistance R1, and diffusion resistance R2. Of these resistance components, the resistance component that causes an instantaneous voltage fluctuation that appears immediately after a current fluctuation is also called instantaneous resistance. The instantaneous resistance is expressed as ohmic resistance R0 or the sum of ohmic resistance R0 and charge transfer resistance R1.

[0059] The ohmic resistance R0 and charge transfer resistance R1 are calculated by measuring the behavior of the current and voltage of the energy storage device when the current is varied. For example, the calculation interval is set to 1 second. The point at which the current is varied during constant-current charging or constant-current discharging is set as the reference (t=0). The ohmic resistance R0 is calculated by dividing the voltage change up to 1 second by the current change. The voltage change after 1 second is further divided by the current change to calculate the sum of the ohmic resistance R0, charge transfer resistance R1, and OCP parameter. The charge transfer resistance R1 is calculated by subtracting the known ohmic resistance R0 and OCP parameter from the resulting sum. The OCP parameter is obtained by calculating the SOC-OCP characteristics of the energy storage device, converting the calculated SOC to the amount of electricity per unit area, and calculating the slope of the potential gradient of the positive electrode, which changes for each unit of electricity.

[0060] FIG. 6 shows an example of the time changes in the SOC, voltage, and current of a storage element during operation. In the upper part of FIG. 6, the horizontal axis represents time (days), and the vertical axis represents SOC (%). In the lower part of FIG. 6, the horizontal axis represents time (msec), and the vertical axis represents voltage (V) or current (A), with the solid line representing the voltage of the storage element and the dashed line representing the current of the storage element. The graph in the lower part of FIG. 6 corresponds to the period indicated by the circle in the graph in the upper part of FIG. 6.

[0061] As shown in the top of Figure 6, the SOC of an energy storage device fluctuates between 0% and 100% as it is charged and discharged during operation. As shown in the bottom of Figure 6, energy storage devices such as ESSs are controlled so that current flows gradually at the start and end of charging or discharging. In contrast, energy storage devices for automotive applications often experience sudden current changes, such as pulse current, at the start and end of charging or discharging. In energy storage devices with gradually fluctuating current, it is difficult to accurately estimate the ohmic resistance that causes voltage fluctuations within a few milliseconds after a current fluctuation, or the charge transfer resistance that causes voltage fluctuations within a few hundred milliseconds.

[0062] In addition, especially when using energy storage devices for purposes such as energy trading, it is expected that they will be continuously charged and discharged at a constant current over a fairly wide SOC range. The instantaneous resistance of the energy storage device depends on the SOC. During normal operation, it is difficult to estimate the instantaneous resistance for intermediate SOC values ​​where a constant current flows without current fluctuations.

[0063] FIG. 7 is a diagram illustrating a method for estimating instantaneous resistance according to this embodiment. In the upper part of FIG. 7, the horizontal axis represents time (days), and the vertical axis represents SOC (%). In the lower part of FIG. 7, the horizontal axis represents time (msec), and the vertical axis represents voltage (V) or current (A), with the solid line representing the voltage of the storage element and the dashed line representing the current of the storage element. The diagram shown in the lower part of FIG. 7 corresponds to the period indicated by the circle in the graph in the upper part of FIG. 7.

[0064] In the estimation method of this embodiment, a sudden fluctuation in current is caused in the storage elements of a specific bank 14 by selectively opening and closing the circuit breaker 42 in the specific bank 14 while the energy storage system 1 is charging or discharging. Fig. 7 shows an example of the case where this estimation method is performed during discharging.

[0065] The estimation method is performed at a certain SOC point during discharge, as shown in the upper part of Figure 7. First, the circuit breaker 42 of the bank 14 including the storage element to be estimated is opened, thereby cutting off current to the storage element. The lower part of Figure 7 shows the operation of the circuit breaker 42. As shown in the lower part of Figure 7, when the circuit breaker 42 is opened, the current value of the storage element becomes zero and the voltage value rises significantly. Based on the time-series data of the voltage measured by the current sensor 44, the voltage rise value at the time of opening and thereafter is calculated, and the calculated voltage rise value is divided by the amount of change in current to determine the return characteristics of the ohmic resistance and the charge transfer resistance.

[0066] When a preset duration has elapsed since the circuit breaker 42 was opened, the circuit breaker 42 is closed, thereby restarting the flow of current to the storage element. When the circuit breaker 42 is closed, the current value of the storage element reaches a set current value, and the voltage value drops significantly. Based on the time-series data of the voltage measured by the current sensor 44, the voltage drop values ​​at the time of closing and thereafter are calculated, and the calculated voltage drop value is divided by the amount of change in current to determine the forward characteristics of the ohmic resistance and the charge transfer resistance.

[0067] The duration of the open state can be set in advance, taking into account the characteristics of the energy storage device. If the duration is too short, it may be impossible to calculate the charge transfer resistance. If the duration is too long, there is a risk of a change in SOC occurring due to current interruption. The duration may be, for example, 10 seconds. With a duration of 10 seconds, it becomes possible to calculate the charge transfer resistance, and there is almost no change in SOC occurring due to current interruption, thereby preventing overcurrent from occurring when current is resumed.

[0068] Because the current value of the storage element when the circuit breaker 42 is open is approximately zero, in the calculation of the instantaneous resistance described above, the amount of change in current at the time of opening and closing is equal to the set current value (absolute value of the current value) that is set in advance in the storage element when energized. If the timing of the opening and closing control of the circuit breaker 42 is known, the instantaneous resistance during opening and closing control can be calculated by measuring only the voltage during opening and closing control, without measuring the current value over time. In other words, the calculation of the instantaneous resistance does not require the current and voltage to be synchronized over time. In this embodiment, the bank BMU 17 itself controls the opening and closing of the circuit breaker 42, so the instantaneous resistance can be estimated by acquiring the voltage during control.

[0069] By varying the timing of the estimation process and performing the above estimation process for storage elements corresponding to different SOCs, instantaneous resistances corresponding to multiple SOCs can be obtained. The SOC of a storage element is automatically calculated by the bank BMU 17 based on measurement data such as the current, voltage, and temperature of the storage element.

[0070] The above describes an example in which the instantaneous resistance is estimated by varying the current by interrupting and restoring the power supply to the storage element during discharge. The instantaneous resistance can also be estimated using a similar method during charging. The return characteristics of the ohmic resistance and charge transfer resistance are obtained by opening the circuit breaker 42 while the storage element is being charged and dividing the voltage drop at and after the opening by the amount of change in current. The forward characteristics of the ohmic resistance and charge transfer resistance are obtained by closing the circuit breaker 42 after a predetermined time has elapsed and calculating the voltage increase at and after the closing and dividing this by the amount of change in current.

[0071] The ohmic resistance and charge transfer resistance obtained by the estimation method can be used for various controls of the energy storage element. As an example, the resistance elements of an energy storage element model, which represents the energy storage element as an electrical circuit, may be corrected based on the estimated ohmic resistance and charge transfer resistance. The energy storage element model combines a voltage source of the energy storage element with circuit elements such as resistors and capacitors to simulate the charge and discharge behavior of the energy storage element. The energy storage element model is described by configuration information indicating the circuit configuration and the values ​​of each element that constitutes the energy storage element model. The values ​​of each element are set in advance based on actual measurement data or the like depending on the purpose of the energy storage element to be simulated.

[0072] For example, the memory unit 172 of the bank BMU 17 stores resistance elements and capacitance elements, including preset ohmic resistances and charge transfer resistances, associated with the SOC and temperature of the energy storage element. When the bank BMU 17 estimates new ohmic resistances and charge transfer resistances using an estimation method, it corrects the known ohmic resistances and charge transfer resistances stored in the memory unit 172 to the newly estimated ohmic resistances and charge transfer resistances. Energy storage element models are often constructed when the energy storage elements are manufactured or when the energy storage system 1 begins operation, and do not reflect the deterioration of the energy storage elements that occurs over long periods of use. By correcting the resistance elements, the current internal state of the energy storage element can be reflected in the energy storage element model, thereby improving the accuracy of the energy storage element model. The ohmic resistances and charge transfer resistances can also be used for various calculations, such as estimating the capacity and predicting deterioration of the energy storage element.

[0073] In this estimation method, the presence or absence of an open fault or a closed fault of the circuit breaker 42 may be determined based on the behavior of the voltage accompanying the opening and closing control of the circuit breaker 42. An open fault refers to a fault in which the circuit breaker 42 remains in the open state despite a switching instruction to close the circuit breaker 42. A closed fault refers to a fault in which the circuit breaker 42 remains in the closed state despite a switching instruction to open the circuit breaker 42.

[0074] For example, after a switching instruction to open the circuit breaker 42 is output, it is possible to determine whether a close fault has occurred by determining whether the amount of voltage change is equal to or greater than a preset threshold. If the amount of voltage change is less than a preset threshold after a switching instruction to open the circuit breaker 42 is output, it is determined that a close fault has occurred. If the amount of voltage change is equal to or greater than a preset threshold, it is determined that a close fault has not occurred. The fault determination may take into account the behavior of the current accompanying the opening and closing control of the circuit breaker 42, and may determine, for example, whether the current value is approximately zero.

[0075] For example, after outputting a switching instruction to close the circuit breaker 42, it is possible to determine whether an open circuit fault has occurred by determining whether the amount of voltage change is less than a preset threshold. If the amount of voltage change is less than the preset threshold after outputting a switching instruction to close the circuit breaker 42, it is determined that an open circuit fault has occurred. If the amount of voltage change is equal to or greater than the preset threshold, it is determined that an open circuit fault has not occurred.

[0076] 8 and 9 are flowcharts showing an example of a processing procedure executed by bank BMU 17. Processing unit 171 of bank BMU 17 executes the following processing in accordance with program 1P stored in memory unit 172. Processing unit 171 may execute the processing of this flowchart in parallel with a process of receiving measurement data including the voltage, current, temperature, etc. of the storage elements from various sensors at predetermined intervals.

[0077] The processing unit 171 of the bank BMU 17 determines whether to start the estimation process (step S11). The processing unit 171 may determine to start the process if a preset start condition is met. Examples of the start condition include a preset start timing, receipt of an instruction to execute estimation, the SOC of the storage element to be processed being a predetermined value or within a predetermined range, or a combination thereof.

[0078] If it is determined not to start the estimation process (S11: NO), the processing unit 171 ends the process. The processing unit 171 may return the process to step S11. If it is determined to start the estimation process (S11: YES), the processing unit 171 determines whether the power storage element is being charged or discharged (step S12). For example, if it is determined that the power storage element is not being charged or discharged because the current (absolute value of the current) acquired from the current sensor 44 is less than a preset current threshold (S12: NO), the processing unit 171 returns the process to step S12 and waits until the power storage element is being charged or discharged.

[0079] For example, if it is determined that charging or discharging is in progress because the current acquired from the current sensor 44 is equal to or greater than a preset current threshold (S12: YES), the processing unit 171 outputs a switching instruction to open the circuit breaker 42 of the own bank 14 (step S13). By switching the circuit breaker 42, the current to the storage element is cut off.

[0080] The processing unit 171 acquires the voltage behavior of the storage element associated with switching of the circuit breaker 42 to the open state by acquiring the measurement values ​​of the voltage sensor 43 at the time of outputting the switching instruction and in the period before and after the output time (step S14). The processing unit 171 calculates the return characteristics of the ohmic resistance and charge transfer resistance of the storage element based on the acquired voltage data and the set current value during charging or discharging (step S15).

[0081] After outputting the switching instruction to switch to the open state, the processing unit 171 determines whether a preset duration has elapsed (step S16). If it is determined that the duration has not elapsed (S16: NO), the processing unit 171 returns the process to step S16 and waits until the duration has elapsed.

[0082] If it is determined that the duration has elapsed (S16: YES), the processing unit 171 outputs a switching instruction to close the circuit breaker 42 of the bank 14 including the storage element to be processed (step S17). By switching the circuit breaker 42, charging or discharging of the storage element is resumed.

[0083] The processing unit 171 acquires the voltage behavior of the storage element associated with switching of the circuit breaker 42 to the closed state by acquiring the measurement values ​​of the voltage sensor 43 at the time of outputting the switching instruction and in the period before and after the output time (step S18). The processing unit 171 calculates the forward characteristics of the ohmic resistance and charge transfer resistance of the storage element based on the acquired voltage data and the set current value during charging or discharging (step S19). The processing of steps S14 and S15 and the processing of steps S18 and S19 may be executed together.

[0084] The processing unit 171 stores the calculated ohmic resistance and charge transfer resistance in the storage unit 172 (step S20). If the SOC and temperature of the power storage element at the time of calculation are known, the SOC and temperature may be stored in association with the ohmic resistance and charge transfer resistance.

[0085] The processing unit 171 calibrates the storage element model by correcting the ohmic resistance and charge transfer resistance associated with the storage element model stored in the storage unit 172 to the newly estimated ohmic resistance and charge transfer resistance values ​​(step S21).

[0086] The processing unit 171 determines whether or not there is an open fault or a closed fault in the circuit breaker 42 based on a change in voltage or current accompanying the opening and closing control of the circuit breaker 42 (step S22). If it is determined that there is no open fault or a closed fault (S22: NO), the processing unit 171 ends the processing.

[0087] When it is determined that an open fault or a closed fault has occurred (S22: YES), the processing unit 171 outputs warning information indicating that an open fault or a closed fault has occurred (step S23). The warning information includes, for example, identification information for identifying the circuit breaker 42 in which a fault has been detected or the bank 14 including the circuit breaker 42, and the fault type. Destinations to which the warning information is output include, for example, a terminal device used by the manufacturer of the power storage system 1, a terminal device used by a maintenance company, etc.

[0088] In the above process, the bank BMU 17 may estimate only one of the return characteristics and the forward characteristics of the instantaneous resistance. The bank BMU 17 may transmit the estimated result of the instantaneous resistance to an external device. The destination of the estimated result includes, for example, the domain BMU 18, the monitoring server 3, a terminal device used by the manufacturer of the energy storage system 1, a terminal device used by a maintenance company, etc.

[0089] The bank BMUs 17 of the banks 14 belonging to the same domain each execute the above-described estimation process at different times, so that the instantaneous resistance of the storage elements in the bank 14 can be estimated for each bank 14 .

[0090] (Second embodiment) In the second embodiment, the configuration of the circuit breaker 42 differs from that of the first embodiment. The following mainly describes the differences from the first embodiment, and the same reference numerals are used to designate the same components as those in the first embodiment, and detailed descriptions thereof will be omitted.

[0091] FIG. 10 shows an example of an electrical connection configuration of the energy storage system 1 of the second embodiment. The energy storage system 1 of the second embodiment includes a circuit breaker 42 configured by a DC / DC converter. The DC / DC converter steps up or down an input voltage to a predetermined output voltage. The circuit breaker 42 converts the voltage so that the current flowing through the bank 14 becomes 0 A, thereby cutting off the power supply to the bank 14. The circuit breaker 42 converts the voltage so that the current flowing through the bank 14 becomes a set current value, thereby restarting the power supply to the bank 14. The circuit breaker 42 may include a switch similar to that of the first embodiment in addition to the DC / DC converter, and may cut off and restore the current by opening and closing the switch together with voltage conversion.

[0092] In the second embodiment, the bank BMU 17 cuts off the power supply to the energy storage elements by instructing the circuit breaker 42 to output a voltage value corresponding to a current of 0 A. The bank BMU 17 resumes the power supply to the energy storage elements by instructing the circuit breaker 42 to output a voltage value corresponding to a set current value.

[0093] The configuration of this embodiment is particularly suitable when the energy storage elements are iron phosphate lithium-ion batteries (hereinafter also referred to as LFP batteries). In an LFP battery, the SOC-OCV (Open Circuit Voltage) profile of the energy storage elements has a wide range of regions (plateau regions) where the voltage value remains almost constant even when the SOC changes. In the plateau region, it is not possible to detect SOC variations between the energy storage elements from the voltages of the individual energy storage elements in the bank 14. Even when there is almost no voltage difference between the energy storage elements, an energy storage element with a low SOC has a lower internal resistance than an energy storage element with a high SOC, and current flows more easily through the energy storage elements.

[0094] Even if the SOCs of the storage elements are the same when current begins to flow, there are variations in the internal resistance of the storage elements depending on their characteristics, so current flows preferentially through storage elements with lower internal resistance rather than storage elements with higher internal resistance, resulting in an imbalance in the SOCs of the storage elements.

[0095] In bank 14, which includes multiple LFP batteries that are prone to imbalance, converting the voltage using a DC / DC converter makes it possible to pass the same constant current through each of the series-connected energy storage elements in bank 14. By passing the same current through each of the series-connected energy storage elements, it is possible to suppress current bias caused by differences in internal resistance and to suppress imbalances between the energy storage elements.

[0096] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The technical features described in each embodiment can be combined with each other, and the scope of the present invention is intended to include all modifications within the scope of the claims and the scope equivalent to the claims. The sequences shown in each embodiment are not limited, and the order of each process may be changed within a range consistent with the present invention, and multiple processes may be executed in parallel. The entity that performs each process is not limited, and the process of each device may be executed by another device within a range consistent with the present invention.

[0097] The matters described in each embodiment can be combined with each other. In addition, the independent claims and dependent claims described in the claims can be combined with each other in any combination, regardless of the reference format. Furthermore, although the claims use a format in which a claim references two or more other claims (multiple claim format), this is not limited to this format. A multiple claim (multi-multi claim) that references at least one other multiple claim may also be used. [Explanation of symbols]

[0098] 100 Estimation System 1. Energy storage system 12 Storage board 14 banks 15 Energy storage module 17 Bank BMU 18 Domain BMU 42 Circuit Breaker 43 Voltage Sensor 44 Current Sensor 171 Processing section 172 Memory section 173 Communications Department 174 Input / output section 1P Program 1A Recording Media

Claims

1. An estimation device for estimating an internal resistance of a storage element in a storage system, the power storage system is configured by connecting a plurality of power storage element groups in parallel, each group including a plurality of power storage elements and a circuit breaker that interrupts current flowing through the power storage elements; acquiring a behavior of the voltage of the storage element in accordance with opening or closing the circuit breaker during charging or discharging of the storage system; An instantaneous resistance indicating an instantaneous internal resistance of the storage element is estimated based on the acquired behavior of the voltage of the storage element. A processing unit for executing processing is provided. Estimation device.

2. During charging or discharging of the power storage system, the behavior of the voltage of the power storage element is acquired when the circuit breaker is opened for a predetermined time and then closed. The estimation device according to claim 1 .

3. outputting an instruction to open or close the circuit breaker; Obtaining the behavior of the voltage of the storage element when the instruction is output The estimation device according to claim 1 or 2.

4. The instantaneous resistance includes ohmic resistance and charge transfer resistance. The estimation device according to claim 1 or 2.

5. A behavior of a voltage of the storage element associated with opening or closing the circuit breaker of one of the storage element groups in the storage system is acquired. The estimation device according to claim 1 or 2.

6. Estimating the instantaneous resistance of each of the storage elements at different SOCs. The estimation device according to claim 1 or 2.

7. The presence or absence of a fault in the circuit breaker is determined based on the behavior of the voltage of the storage element. The estimation device according to claim 1 or 2.

8. The circuit breaker is a DC / DC converter. The estimation device according to claim 1 or 2.

9. A power storage system includes a plurality of parallel-connected storage element groups and an estimation device, the energy storage element group includes a plurality of energy storage elements and a circuit breaker that interrupts current flowing through the energy storage elements; The estimation device includes: Obtaining a behavior of the voltage of the storage element when the circuit breaker is opened or closed while the storage element group is being charged or discharged; An instantaneous resistance indicating an instantaneous internal resistance of the storage element is estimated based on the acquired behavior of the voltage of the storage element. A processing unit for executing processing is provided. system.

10. A method for estimating an internal resistance of a storage element in a storage system, comprising: the power storage system is configured by connecting a plurality of power storage element groups in parallel, each group including a plurality of power storage elements and a circuit breaker that interrupts current flowing through the power storage elements; acquiring a behavior of the voltage of the storage element in accordance with opening or closing the circuit breaker during charging or discharging of the storage system; An instantaneous resistance indicating an instantaneous internal resistance of the storage element is estimated based on the acquired behavior of the voltage of the storage element. Estimation method.

11. A program for estimating an internal resistance of a storage element in a storage system, the power storage system is configured by connecting a plurality of power storage element groups in parallel, each group including a plurality of power storage elements and a circuit breaker that interrupts current flowing through the power storage elements; On the computer, acquiring a behavior of the voltage of the storage element in accordance with opening or closing the circuit breaker during charging or discharging of the storage system; An instantaneous resistance indicating an instantaneous internal resistance of the storage element is estimated based on the acquired behavior of the voltage of the storage element. A program that executes a process.

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